This invention relates to a stable and calibratable fluid bleed unit which can be used as a controlling element in air/fuel control systems for turbocharged carbureted natural gas reciprocating engines. Presently, compressed air from the turbocharger is used as a loading pressure on the spring or setpoint side of the gas pressure regulator. Gas pressure to the carburetor is then automatically increased when more air produced by the turbocharger and this combined with the design of the carburetor keeps the air/fuel ratio about constant. This is not quite good enough, however, for obtaining maximum life from a catalytic converter when used, and for minimizing pollution.
The current controlled fluid bleed device of this invention is used to bleed and reduce the air pressure applied to the setpoint side of the fuel gas regulator, set to run the engine slightly rich, so as to trim the air/fuel ratio in response to the current output of a proportional plus integral controller. This results in more perfect control of the air/fuel ratio.